In the capital, students sang songs before offering flowers at the royal palace.

"In the king's whole life, whatever he did was for the country, not for himself," Lay Rithiya, a law student, told Reuters news agency.

"So we are here to mourn him and we consider that he is a hero and I have never had this sadness in 20 years."

Officials from the US, China, North Korea, Japan and other countries have also sent messages of condolence.

Funeral plans

Sihanouk's widow, Queen Monique, held hands with her son, King Norodom Sihamoni, as they emerged from the plane carrying the former king's body when it touched down at Phnom Penh earlier on Wednesday.

Analysis

By Jonathan HeadBBC News, Phnom Penh

All the people I spoke to - young and old - spoke of Sihanouk as the man who built their country, delivering it from French colonial rule, and then defended its sovereignty from the predations of bigger neighbours and superpowers.

No-one mentioned his preening vanity, his capriciousness and his love of worldly pleasures.

He was, after all, a survivor, in a nation of survivors. Twice abdicated, once deposed by a coup, and for four years a prisoner of the Khmer Rouge. If he compromised and broke promises, so did many others here.

In a country which has endured so many wrenching changes, Sihanouk was a constant presence. And now he has gone.

Monks chanted prayers as the coffin, decked with white flowers, was brought out of the plane.

The queen wore the traditional mourning clothes of a white shirt and black skirt, and throngs of similarly dressed mourners waved Cambodian flags along the coffin's route to the royal palace.

Sihanouk's body will lie in state at the palace for three months before an elaborate funeral and cremation, said the government.

The government has ordered all radio and television stations to refrain from broadcasting any programmes that may be deemed inappropriate during the mourning period.

Sihanouk became king in 1941 while still a teenager, and led Cambodia to independence from France in 1953.

He was a presence through decades of political and social turmoil in Cambodia, despite long periods of exile overseas.

In later life he emerged as a peacemaker who helped bring stability back to his country, after an ill-fated choice to back the Khmer Rouge in its early years.

He remained an influential figure in his country, despite his abdication in 2004 in favour of his son King Norodom Sihamoni.